It is sometimes necessary to plug holes formed in fluid-carrying bodies. For example, manifolds used in hydraulic control systems often have holes which must be sealed to prevent fluid from leaking into or out of the fluid-carrying body.
One prior art device employed for hole closure purposes is known as the Lee plug and includes a plug having a tapered axial hole extending part way through the plug and a tapered pin. The plug, which has its inner end closed, is slipped into a counterbore of the passage to be sealed until its inner end engages the shoulder of the counterbore. The tapered pin is then pounded or pressed into the hole in the plug to expand the plug radially into sealing tight contact with the wall of the counterbore.
One problem with this construction is that the use of a hammer or press to drive the tapered pin into the plug does not provide adequate control over the forces on the plug or the fluid-carrying body during installation. This can lead to structural failure during installation or to undesirable residual stresses. The need for a counterbore and a shoulder in the fluid-carrying body is also undesirable because it requires an additional work operation. In addition, the diameter of the counterbore is larger than the diameter of the remaining portion of the passage to be sealed, and this is undesirable because, when the counterbore is formed in a boss, it reduces the wall thickness of the boss thereby reducing its strength. The wall thickness of the boss can be enlarged, but this adds a weight and size penalty which is extremely undesirable for aircraft applications.
A second prior art pressure plug includes a sleeve open at both ends and a tapered plug. The sleeve has a tapered bore, and the tapered plug has a threaded socket at the small diameter end thereof. To install this pressure plug, the sleeve is placed in the passage to be sealed and a threaded pulling tool is threaded into the socket of the plug. With the sleeve suitably restrained against axial movement, the plug is forcibly pulled into the tapered bore of the sleeve to seal the interfaces between the plug and the sleeve and between the sleeve and the wall of the passage to be sealed. The tapered surfaces of the plug and sleeve are arranged so that they taper radially inwardly as they extend toward the outer end of the passage to be sealed.
Unfortunately, this prior art device also does not provide for accurately and positively controlling the forces of installation. In addition, the wall defining the threaded socket in the plug may be deformed radially inwardly as a result of installation thereby making the removal of the installation tool from the plug somewhat difficult. The threaded socket in the plug may also tend to reduce the effectiveness of that portion of the plug in forcing the sleeve radially outwardly.